Antibacterial resistance is an increasingly serious threat to global public health. In recognition of this threat, the President's Council of Advisors n Science and Technology (PCAST) has just submitted a report to President Obama underscoring the urgency of ensuring an effective arsenal of antibiotics that is continuously renewed. Two pathogens recently identified by the CDC as major antibiotic resistance threats in the United States are methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant S. aureus (VRSA). This proposal is premised on the hypothesis that developing new antibiotics with novel mechanisms of action will provide an innovative and effective therapy against MRSA and VRSA infections. The proposed project will develop drugs that act against a new antibacterial target (a protein essential for bacterial cell division termed FtsZ) unexploited by ay antibiotics in current clinical use. The proposal incorporates innovative solutions to problems of drug administration, elimination, and resistance that have hindered early efforts to develop drugs targeting bacterial cell division. Significantly, strong preliminary results are presented tht provide validation for the innovative approach. The three areas to be investigated in this project are: 1. Identification of compounds that improve antibiotic efficacy. A problem associated with FtsZ-targeting compounds that have been generated to date is rapid elimination due to liver metabolism. This aim is geared toward the synthesis and evaluation of new compounds designed for resistance to liver metabolism and thus longer durations of action and enhanced efficacy in vivo. 2. Can other antibiotics function synergistically with our compounds? Synergistic combination therapy is an effective strategy for enhancing in vivo efficacy, while also minimizing the potential for toxicity and emergence of drug resistance. We hypothesize that our FtsZ-targeting compounds should act synergistically with drugs that target the penicillin binding proteins (PBPs), since both the PBPs and FtsZ play important roles in a common pathway leading to bacterial cell division. This aim is geared toward identifying PBP-targeting antibiotic that act synergistically with our FtsZ-targeting compounds. 3. Selection of promising preclinical drug candidates. A critical step toward the selection of a preclinical candidate is a pharmacological safety assessment for potential toxicities. This aim is geared toward toxicological evaluation of our lead compounds with regard to mammalian cytotoxicity, genotoxicity (Ames mutagenicity), cardiotoxicity (hERG potassium channel inhibition), and single-dose acute toxicity. Together, these investigations will culminate in the selection of preclinical drug candidates primed for benchmarking Investigational New Drug (IND) studies. Ultimately, this will improve clinical practice by providing a new therapy for the treatment of multidrug-resistant (MDR) staphylococcal infections that will be effective even when current standard-of-care drugs fail.